The present invention relates to a process for enhancing the reliability and consistency of biological effectiveness of an exogenous chemical substance applied to foliage of a plant. The process involves application of a compound from the anthraquinone and substituted anthraquinone family (herein referred to as anthraquinone compounds) to the foliage, either sequentially or simultaneously with the exogenous chemical substance. The invention also relates to plant treatment compositions comprising an exogenous chemical substance and an anthraquinone compound.
For many purposes in agriculture and related endeavors it is desired to treat plants with exogenous chemical substances of various kinds. An exogenous chemical substance as defined herein is a chemical substance, whether naturally or synthetically obtained, which is applied to a plant with the intent or result of delivering the substance to one or more sites in the plant where the substance expresses some desired biological activity. Examples of exogenous chemical substances include, but are not limited to, chemical pesticides (such as herbicides, algicides, fungicides, bactericides, viricides, insecticides, miticides, nematicides and molluscicides), plant growth regulators, fertilizers and nutrients, gametocides, defoliants, desiccants, mixtures thereof and the like.
Many exogenous chemical substances are applied to foliage (ie. leaves and other non-woody above-ground parts) of a plant, and have a site of action in the plant either close to or remote from the locus of application. Such substances are referred to herein as foliar-applied exogenous chemical substances. Typically, by plant treatment methods known in the art, only a small portion of the amount of an exogenous chemical substance applied to foliage reaches sites of action in the plant where the biological effect of the exogenous chemical substance can be usefully expressed. It is therefore a major desideratum in agriculture and related endeavors to enhance the efficiency of delivery of foliar-applied exogenous chemical substances to their sites of action in plants, and thereby to enhance the biological effectiveness of the exogenous chemical substance for the purpose for which it is used.
Application to foliage of an exogenous chemical substance by methods known in the art does not universally result in inefficient delivery to sites of action. In some situations such methods provide excellent biological effectiveness, even at low use rates of the exogenous chemical substance. The problem is that it is seldom possible to identify those situations in advance, partly because so many factors influence delivery efficiency. These factors include weather (temperature, relative humidity, daylength, cloudiness, precipitation, wind, etc.) preceding, during and following application, soil conditions (fertility, aeration, etc.), plant growth stage, health and physiological status, equipment-related inaccuracies in application, and other factors. Therefore, to help ensure reliable and consistent biological effectiveness of a foliar-applied exogenous chemical substance, the user typically applies the substance at a higher rate than truly necessary in the majority of situations.
Benefits of a method giving greater reliability include an ability to reduce rates of application of exogenous chemical substances without sacrificing consistency of biological effectiveness. Pressures felt by the agricultural industry to reduce pesticide, particularly herbicide, usage are well evidenced by symposia on the subject, such as that held in 1993 by the Weed Science Society of America and documented in Weed Technology 8, 331-386 (1994). Reduced use rates bring rewards not only environmentally but also economically, as the cost per unit area treated decreases.
Herbicidal compositions have been described containing chemical synergists which have been hypothesized to enhance herbicidal effectiveness by affecting metabolic processes of the plant. Such chemical synergists have included 6-benzylaminopurine, gibberellic acids, and 2-choroethylphosphonic acid, all known to have plant growth regulating activity in their own right. For example, some researchers have reported that if gibberellic acids are applied to growing plants at some time prior to the application of a glyphosate herbicide composition, the herbicidal effectiveness of the glyphosate is increased. However, the use of some synergists such as 6-benzylaminopurine, gibberellic acids, and 2-choroethylphosphonic acid is limited because of the need to apply the synergist days or even weeks before the application of the herbicide. Other synergists, while capable of being applied simultaneously with the herbicide, are effective only at high concentrations, e.g., 1:1 or 2:1 ratios by weight of the exogenous chemical substance to synergist.
A widely practiced method of enhancing reliability of biological effectiveness of a foliar-applied composition of an exogenous chemical substances, particularly a herbicide, is to add an enhancing agent comprising an ammonium salt, most commonly ammonium sulfate, to the composition being applied. It is well known to those practicing this method that enhanced biological effectiveness is not assured with every use; however the low cost of the method means that even if biological effectiveness is enhanced in only a small proportion, for example 1 in 5, of times the method is used, it is still worthwhile.
There are limitations to the usefulness of ammonium salts as enhancing agents resulting from the relatively high rates that have to be used. Ammonium sulfate, for example, is typically used at concentrations in an aqueous application solution of 1-5% weight/volume, for example around 2% weight/volume. Common spraying equipment used in agriculture applies a spray volume of 50-1000 liters per hectare (1/ha) of solution; at a typical spray volume of 200 l/ha containing 2% ammonium sulfate, the use rate of ammonium sulfate is 4 kg/ha. Such a high use rate leads to inconvenience for the user and difficulties for the formulator desiring to provide a product combining both an exogenous chemical substance and an enhancing agent based on ammonium sulfate.
Most exogenous chemical substances are designed to be used at much lower rates than those shown above for ammonium sulfate, for example 1-1000 grams of active ingredient per hectare (g a.i./ha). Thus, in an application method using ammonium sulfate, the amount of ammonium sulfate used is typically much greater than the amount of the exogenous chemical substance. It is consequently uneconomic in most situations for the manufacturer of the exogenous chemical substance to supply a useful amount of ammonium sulfate preformulated with the exogenous chemical substance. Economics in the agricultural pesticide business, for example, mandate that the pesticide be formulated at as high a concentration or loading as possible to minimize packaging, shipping and storage costs. The requirement to coformulate a large amount of ammonium sulfate with the pesticide active ingredient is inconsistent with achieving a high loading of active ingredient.
It is therefore an objective of the present invention to provide an agent that enhances the reliability of effectiveness of foliar applied exogenous chemical substances but that achieves this at much lower use rates than is the case with ammonium sulfate.
Many studies have been conducted in pursuit of this elusive goal. As biological effectiveness of an exogenous chemical substance depends upon delivery of the substance into living cells or tissues of the plant, some investigators have focused the search for a low-rate enhancing agent on classes of compounds which, at low rates, can be expected to stimulate various biological processes in plants. U.S. Pat. No. 4,436,547 to Sampson discloses that additives to improve the action of agricultural chemicals can include a carbohydrate source or organic acid to supply metabolizable energy or as precursors of amino acids and nucleotides, a vitamin or coenzyme to stimulate metabolic processes, a nucleic acid precursor to stimulate nucleic acid synthesis, a fatty acid (or fat or oil that can be degraded thereto) as precursor of molecules required in growth processes, an amino acid as structural unit for protein synthesis, and a naturally occurring plant growth regulator to affect metabolism in such a way as to render an applied pesticide more effective. In the case of herbicides, it is postulated in the above cited patent that "by stimulating growth and uptake of applied chemicals it is possible to enhance the activity of a number of herbicides, especially against older more established weeds."
The present invention provides a process for enhancing biological effectiveness of a foliar-applied exogenous chemical substance involving an enhancing agent not contemplated by Sampson, namely an anthraquinone compound as herein defined.